In the description of the background of the present invention that follows reference is made to certain structures and methods, however, such references should not necessarily be construed as an admission that these structures and methods qualify as prior art under the applicable statutory provisions. Applicants reserve the right to demonstrate that any of the referenced subject matter does not constitute prior art with regard to the present invention.
The notation, MAX-phases, is used for a wide range of ceramic materials based on the formula Mn+1AXn wherein M is a transition metal, A is Si, Al, Ge or Ga and X is C, N or B. In the case that X is N only, Mn+1ANn, they are referred to as MAN-phases. This family of materials has a hexagonal crystal structure and nanolaminated constitution from large unit cells. The MAX- and MAN-phases are characterized by the low content of non-metallic atoms compared to metallic atoms, i.e.—for n=1; 25 at %, n=2; 33 at % and n=3, 37.5 at %.
The preparation of MAX-phases in form of bulk material of the Ti3SiC2 phase was first reported in 1967 by Nowotny, Monatsh für Chem. 98:329–337 (1967).
In 1972, Nickl et al, J. Less-Common Metals 26:335 (1972), reported that they have grown Ti3SiC2 by chemical vapor deposition (CVD) using the reactive gases SiCl4, TiCl4, CC14 and H2. Later also Goto et al., Mat. Res. Bull. 22:1195–1201 (1987), reported growth of Ti3SiC2 by a CVD process based on the same reactive gases as Nickl et al. at a deposition temperature between 1300 and 1600° C.
The possibility to grow pure phase single-crystal Ti3SiC2 using PVD technique on single crystal MgO (111) substrates by epitaxial growth have been reported by Seppänen et al (Proc. Scandinavian Electron Microscopy Society, Tampere, Finland, 11–15 June, 2002, s 142–143 ISSN 1455–4518. Three different techniques were reported (i) unbalanced DC magnetron sputtering from elemental targets; (ii) unbalanced magnetron sputtering from elemental target and evaporation of C60; and (iii) unbalanced magnetron sputtering from stoichiometric target.
The anisotropic hardness of the MAX phase Ti3SiC2 single crystals where first reported by Nickl et al, J. Less-Common Metals 26:283 (1972).
A review of mechanical properties of MAX-phases is made by M. W. Barsoum, Solid St. Chem., Vol. 28 (2000) 201–281. Several unusual properties that are beneficial for applications of ceramics were reported for the Ti3SiC2 bulk material including high toughness, high flexural strength, crack growth resistance, cyclic crack growth resistance, etc.
U.S. Pat. No. 5,942,455 discloses a process to produce bulk products having single phases or solid solutions of the formula M3X1Z2 wherein M is a transition metal, X is Si, Al or Ge and Z is B, C or N by taking a powdered mixture containing M, X and Z to a temperature of about 1000° C. to about 1800° C. The products so formed have excellent shock resistance, oxidation resistance and machinability.
U.S. Pat. No. 6,013,322 discloses a surface treatment by contacting the surface of a “312-compound” (e.g.—Ti3SiC2) ternary ceramic material with a surface-modifying compound selected from carburization agents, silicidation agents, nitridation agents and boronization agents, at an elevated temperature of at least about 600° C. for a period of time sufficient to provide a surface reaction layer of at least about one micron in thickness in the surface-treated material.
In the system of Ti/Al and other transition metal nitrides, carbides and oxides many patents occur, e.g.—for single layers, e.g.—U.S. Pat. No. 5,549,975, multi-layers, e.g.—U.S. Pat. No. 5,330,853, gradients, e.g.—EP 448,720, or combinations thereof, e.g.—U.S. Pat. No. 5,208,102. However, all those materials are close to stoichiometry between the metallic and non-metallic elements of the NaCl-type cubic phase, i.e. −50 at %.